I suppose having a good description of what I'd like to do might help: I'd like to be able to make an N-Tuple an instance of a type class.
 
class Foo a where
    ....
 
instance Foo (,) where
    ....
 
instance Foo (,,) where
    ....
The different kindedness of (,) and (,,) prevent this from working.
 
/jve

 
On Mon, Mar 30, 2009 at 2:00 PM, Martijn van Steenbergen <martijn@van.steenbergen.nl> wrote:
John Van Enk wrote:
 > Haskell not having 'polymorphic kinds'.
 Is there a good description of why Haskell doesn't have polymorphic kinds?

IANA expert but polymorphic kinds belong to a set of reasonably new influences (e.g. from dependently typed programming languages and generic programming) and they haven't been 1) polished enough to be a widely accepted standard or 2) simply haven't been implemented yet (low priority, etc).

Besides that, I sometimes see polymorphic kinds in GHC error messages, so I suspect that at least parts of GHC already support them.

Martijn.




--
/jve